Battery

ABSTRACT

The battery has an electrode assembly inserted into a cylindrical external case. A lead plate connected to the electrode assembly is weld attached to the inner surface of the external case by an energy beam applied from outside the external case. The external case has a projection jutting from its inner surface. The energy beam is applied to the projection from outside the external case and weld attaches the lead plate to the inner surface of the projection.

[0001] This application is based on application No.10-245119 filed inJapan on Aug. 31, 1998, the content of which incorporated hereinto byreference.

BACKGROUND OF THE INVENTION

[0002] This invention relates to a battery in which a lead (anelectrically conducting lead, not the element Pb) plate connected to anelectrode assembly is welded to the bottom plate of an external case byan energy beam such as a laser.

[0003] The following describes fabrication of a prior art battery inwhich a lead plate connected to an electrode assembly is welded to thebottom plate of an external case.

[0004] (1) A laminate of positive electrode plate, negative electrodeplate, and separator in between, is rolled into a spiral shape to formthe electrode assembly. The spiral shaped electrode assembly is formedwith a center hole to insert an electrode rod for weld connection.

[0005] (2) The electrode assembly is inserted into a circularcylindrical external case with a bottom.

[0006] (3) A lead plate connected to the bottom of the electrodeassembly is weld attached to connect it to the bottom of the externalcase. As shown in FIG. 1, an electrode rod 2 for weld connection isinserted into the electrode assembly 1 center hole, and the lead plate 4is pushed by the electrode rod 2 against the bottom plate of theexternal case 5 and welded.

[0007] (4) A lead plate which draws out of the top of the electrodeassembly 1 is connected to an electrode on a sealing lid which closesoff the opening at the top of the external case 5. After the externalcase is filled with electrolyte, the sealing lid is fixed to the openingin the external case. The external case is sealed in an airtight fashionby the sealing lid.

[0008] This process has the characteristic that the lead plate 4connected to the electrode assembly 1 can be reliably welded and fixedto the bottom plate of the external case 5. However, a battery of thisconfiguration must be provided with a center hole in the middle of theelectrode assembly 1, and this center hole must have a diameter largerthan the electrode rod for weld connection. Therefore, the actual volumeof the electrode assembly is reduced and the battery's capacity isdecreased. Increasing battery capacity by reducing the size of theelectrode assembly center hole may be considered, but when center holesize is reduced, fitting the electrode rod in the center hole becomes aproblem.

[0009] Technology for connecting a lead plate to the bottom of anexternal case by laser welding from outside the case has been developedto eliminate the drawbacks of a battery with the configuration describedabove (Japanese Non-examined Patent Publications No. 4-162351 issued onJun. 5, 1992 and No. 8-293299 issued on Nov. 5, 1996). These and otherdisclosures cite batteries which do not use an electrode rod for weldconnection. As shown in FIG. 2, an energy beam such as a laser isapplied to the bottom plate 25A of the external case 25 from outside thecase. The energy beam fuses a portion of the bottom plate 25A and thelead plate 24 to weld and attach the lead plate 24 to the bottom plate25A.

[0010] As shown in FIG. 2, there is no need to provide a center hole inthe electrode assembly 21 of a battery in which an energy beam such as alaser beam is applied from outside the case to weld the lead plate tothe bottom plate. Consequently, this type of battery has thecharacteristic that the actual electrode assembly volume and batterydischarge capacity can be increased. However, in this type of battery inwhich the lead plate is weld attached from outside the external case,the lead plate can fail to reliably weld attached to the bottom plate.For example, with the electrode assembly inserted into the externalcase, if the lead plate is separated from the bottom plate, the bottomplate of the external case will fuse but the lead plate will not, andthe energy beam will not be able to reliably weld attach the lead plateto the bottom plate. In addition, if foreign material or contaminationis between the lead plate and bottom plate, the energy beam will alsofail to make a reliable weld attachment. In particular, whether or notthe lead plate is weld attached to the bottom plate and what kind ofattachment is made cannot be determined from outside this type ofbattery. Since evaluation of battery quality is difficult, it isextremely important to make weld attachments more reliably.

[0011] This invention was developed to solve these types of problems. Itis thus a primary object of the present invention to provide a batterythat can reliably weld attach a lead plate to an external case.

[0012] The above and further objects and features of the invention willmore fully be apparent from the following detailed description withaccompanying drawings.

SUMMARY OF THE INVENTION

[0013] The battery has an electrode assembly inserted into a cylindricalexternal case. A lead plate connected to the electrode assembly is weldattached to inner surface of the external case by an energy beam appliedfrom outside the external case.

[0014] Further, the battery of the present invention is provided with aprojection which projects from the inner surface of the external case.An energy beam is applied to the projection from outside the externalcase to weld attach the inner surface of the projection to the leadplate.

[0015] A battery of this configuration has the characteristic that thelead plate can be reliably weld attached to the external case. This isbecause the projection in the external case makes reliable contact withthe lead plate. The external case and lead plate can be reliably weldattached by application of an energy beam, such as a laser, to theprojection which has its inner surface in contact with the lead plate.In particular, a battery, in which the lead plate and external case canbe reliably contacted and welded, also reliably prevents separation ofthe lead plate and external case due to mechanical shock.

[0016] In the battery of the present invention, the projection isdisposed in a still more preferable arrangement for contact and weldattachment to the lead plate by curving the projecting surface to itscenter or by making a conical shaped projection.

[0017] Further, the lead plate of the battery can be provided with aflexible deforming piece, and the projection in the external case can beweld attached to this flexible deforming piece. In addition, theflexible deforming piece can jut outwards towards the projection in theexternal case to further improve connection of the lead plate and theexternal case.

[0018] Anti-corrosive coating can be used to coat the region of thebattery where the energy beam is applied from outside the external case.This effectively prevents corrosion of the region of energy beamapplication, and contact resistance problems can be avoided via theanti-corrosive coating.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a cross section view showing a prior art batteryfabrication method.

[0020]FIG. 2 is a cross section view showing another fabrication methodof a prior art battery.

[0021]FIG. 3 is a cross section view showing an embodiment of a batteryof the present invention.

[0022]FIG. 4 is a cross section view showing the bottom of the externalcase of the battery shown in FIG. 3.

[0023]FIG. 5 is a cross section view showing the bottom of the externalcase of a battery of another embodiment of the present invention.

[0024]FIG. 6 is a bottom view of the external case shown in FIG. 4.

[0025]FIG. 7 is a cross section view showing the bottom region of abattery of another embodiment of the present invention.

[0026]FIG. 8 is a plan view showing the lead plate contained at thebottom of the battery shown in FIG. 3.

[0027]FIG. 9 is a plan view showing the lead plate contained at the topof the battery shown in FIG. 3.

[0028]FIG. 10 is an enlarged cross section view of a lead plate.

[0029]FIG. 11 is a cross section view showing the disposition of a leadplate for weld attachment to an electrode assembly.

[0030]FIG. 12 is a front view showing another type of lead plate forincorporation into a battery of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0031] The battery shown in FIG. 3 is a rechargeable battery such as anickel hydride battery, a nickel cadmium battery, or a lithium ionbattery, and is provided with a circular cylindrical external case 35,an electrode assembly 31 for insertion into this external case 35, andlead plates 33, 34 for connecting the electrode assembly 31 to theexternal case 35. Although the external case of the battery shown inFIG. 3 has a circular cylindrical shape, the external case of thebattery of the present invention is not limited to a circularcylindrical shape. Although not illustrated, the external case may alsotake on, for example, a rectangular cylindrical shape or an ellipticalcylindrical shape.

[0032] The external case 35 is made of iron or steel with nickel platedsurfaces. The material for the external case 35 is the optimum metalselected considering the type of battery and its characteristics. Forexample, the external case 35 may also be made of stainless steel,aluminum, or aluminum alloy. The open region at the upper end of themetal external case 35 is sealed closed in an airtight fashion by thesealing lid 37. The sealing lid 37 of FIG. 3 is fixed in place on theexternal case 35 in an electrically insulating fashion by a caulkedjunction structure. The sealing lid may also be fixed on the externalcase in an airtight fashion by a method such as laser welding. Thisconfiguration of sealing lid insulates and holds an electrodestationary. The sealing lid 37 fixes one terminal of the battery inplace.

[0033] As shown in FIGS. 3 and 4, the external case 35 is provided witha projection 35 a in the region where the lead plate 34 is welded andfixed to the external case 35. A projection 35 a is provided on thebottom plate 35A of the external case 35 of the battery shown in thefigures, and the lead plate 34 is weld attached to this projection 35 a.As shown in the bottom view of FIG. 6, the external case 35 is providedwith a projection 35 a at the center of the bottom plate 35A. Anexternal case 35 provided with a projection 35 a in this location hasthe characteristic that the location for weld attachment of the leadplate 34 by an energy beam operation such as laser welding can be easilyand accurately aligned. This is because the location for energy beamweld attachment of the lead plate 34 does not change regardless of theposition to which the external case 35 has rotated. However, there is norequirement to locate the projection at the center of the bottom plate.Further, the projection is not required to be provided on the bottomplate. For example, as shown in FIG. 7, the projection may also beprovided on a side-wall of the external case 75. However, regardless ofwhere the projection is provided, the lead plate 74 is weld attached tothe projection 75 a.

[0034] The outside diameter of the projection 35 a is designed to anoptimum value considering the area of the weld attach. If the diameterof the projection 35 a is made small, the top of the projection can bereliably weld attached to the lead plate. However, if the projectiondiameter is too small, the weld attach area between the lead plate andexternal case becomes smaller.

[0035] Making the projection 35 a jut high up from the inner surface ofthe external case 35 improves the situation for weld attachment of theprojection 35 a and the lead plate 34. However, making the projection 35a project high upwards pushes the electrode assembly 31, which insertsinto the external case 35, upwards. Consequently, this makes itnecessary to reduce the height of the electrode assembly 31, and thisreduces the real capacity of the electrode assembly.

[0036] As shown in Fig, 4, the projection 35 a is shaped with its convexsurface curved around the central protrusion. Or, as shown in FIG. 5,the projection 55 a protrudes outward in a conical shape. In a batterywith a projection having a protruding surface in one of theseconfigurations, the lead plate 54 contacts the projection 55 a withoutgaps or voids. Therefore, a battery of this type has the characteristicthat the lead plate 54 and projection 55 a can be more reliably weldattached. However, the protruding surface of the projection 55 a mayalso be planar.

[0037] The electrode assembly 31 is a laminate of a positive electrodeplate, a negative electrode plate, and a separator in between. Thebattery shown in FIG. has a stack of positive electrode plate, negativeelectrode plate, and intervening separator rolled together. This spiralshaped electrode assembly 31 is inserted into the circular cylindricalexternal case 35. The spiral electrode assembly 31 may also be pressedfrom both sides to distort it into an elliptical shape for insertioninto an elliptical shaped or rectangular shaped external case. Further,an electrode assembly for insertion into a square cylindrical externalcase can also be fabricated by cutting a plurality of positive electrodeplate and negative electrode plate sheets, and stacking them withseparator in between.

[0038] The electrode assembly 31 has lead plates 33, 34 connected to thepositive and negative electrode plates. The lead plates 33, 34 aredisposed at the top and bottom of the electrode assembly 31 and areconnected to the positive and negative electrode plates. As shown inFIG. 3, positive and negative electrode plate core material projectsupward and downward from the electrode assembly 31, and the lead plates33, 34 are connected to these projections. In the electrode assembly 31in the figures, the electrode plate 34 disposed at the bottom of theelectrode assembly 31 is connected to the external case 35. Theelectrode plate 33 disposed at the top of the electrode assembly 31 isconnected to the sealing lid 37.

[0039] As shown in FIGS. 8 and 9, the lead plates 33, 34, which connectto the top and bottom of the electrode assembly 31, are cut from metalplate in disk shapes smaller than the inside of the external case 35. Asshown in FIG. 9, the lead plate 33 which connects to the top surface ofthe electrode assembly 31 has a lead strip 33A projecting from itsperiphery. The lead strip 33A connects to the sealing lid 37, which iselectrically insulated from, and attaches to the open region of theexternal case 35. A lead plate 33 of the shape shown in FIG. 9 may alsobe used to connect the bottom surface of the electrode assembly to aside-wall of the external case.

[0040] As shown in the cross section view of FIG. 11, these types oflead plates 33, 34 are pressed against the electrode assembly 31 via awelding electrode 38, and reliably connected by resistive electricwelding. A plurality of holes 39 are opened through the lead plates 33,34 shown in FIGS. 8 and 9 to reliably connect the lead plates 33, 34electrically to the electrodes of the electrode assembly 31. As shown inthe enlarged cross section view of FIG. 10, projections 310 are providedextending downward from the periphery of the holes 39 in the lead plates33, 34. The projections 310 are connected to the electrode plates of theelectrode assembly. Further, as shown in FIG. 9, the lead plate 33,which connects to the top of the electrode assembly 31, is provided withslits 313 on either side of a center hole 311 to reduce unnecessaryelectric current during resistive electric welding.

[0041] As shown in FIG. 8, the lead plate 33, which connects to the topof the electrode assembly 31, is provided with a U-shaped cut-out 312,and a flexible deforming piece 34A is provided inside this cut-out 312.The flexible deforming piece 34A protrudes outwards towards theprojection 35 a in the external case 35. The flexible deforming piece34A is approximately at the center of the lead plate 34, and is weldattached to the external case 35 projection 35 a.

[0042] Since lead plates 33, 34 in a battery of this configuration canconnect to the electrode assembly 31 at a plurality of locations, thebattery has excellent high current characteristics. This is becauseinternal resistance can be made small. Further, a battery of thisconfiguration also has the characteristic that the lead plate 34 can bereliably weld attached to the bottom plate 35A via an energy beam. Thisis because the electrode assembly 31 can be inserted into the externalcase 35 and the lead plate 34 can be put in intimate contact with thebottom plate 35A of the external case.

[0043] However, the battery of the present invention is not limited to alead plate, which connects the electrode assembly to the external case,according to the structure described above. For example, the lead platemay also have a band shape as shown in FIG. 12. This lead plate 124connects to exposed core material of an electrode, extends out from thebottom of the electrode assembly, and its end weld attaches to the innersurface of the external case. This type of lead plate 124 may alsoextend out from the side of the electrode assembly and weld attach to aside-wall of the external case as shown in FIG. 7.

[0044] The lead plate 34 is weld attached to the inner surface of theexternal case 35. An energy beam such as a laser beam or an electronbeam, etc. is used as a method of weld attaching the lead plate 34. Theenergy beam fuses both the external case 35 and the lead plate 34 toweld attach the lead plate 34 and the external case 35. As shown in FIG.4, a laser beam is shined at a wide region, which includes the entireprojection 35 a, to weld attach the lead plate 34 and the external case35.

[0045] When an energy beam such as a laser beam is applied to the outersurface of the external case 35, corrosion resistant metal plating,which coats the surface of the external case 35, loses itseffectiveness. Consequently, the region of energy beam application caneasily corrode. This drawback can be eliminated by coating the region ofenergy beam application with an anti-corrosive coating 36, as shown inthe enlarged portion of the cross section view of FIG. 3. However, whenanti-corrosive coating 36 is applied to the bottom surface of theexternal case 35, the anti-corrosive coating 36 can be the cause ofcontact resistance during battery operation. This is becausenon-conducting organic coating material is used as the anti-corrosivecoating 36. This drawback can be eliminated by mixing conductivematerial such as carbon or metallic powder into the anti-corrosivecoating 36.

[0046] The anti-corrosive coating 36 can be sprayed in aerosol form orapplied using a paint brush. Further, the anti-corrosive coating 36 mayalso be sprayed from a miniature nozzle according to ink-jet technology.The ink jet method has the characteristic that a precise thickness ofanti-corrosive coating can be applied to the precise location of energybeam application. In addition, the anti-corrosive coating 36 can also beapplied at the same time the date of manufacture and the usable date areprinted on the external case of the battery by ink-jet.

EMBODIMENTS Embodiment 1

[0047] Nickel cadmium batteries were fabricated by the followingprocess, and lead plate to external case connections were tested. Anexternal case provided with a projection 35 a in the center of thebottom surface, as shown in FIG. 4, was used. The projection 35 a wasshaped with its convex surface curved around the central protrusion. Theoutside diameter of the projection 35 a was approximately 2 mm, theheight of the projection was 0.2 mm, and the radius of curvature of theprotruding surface was 15 mm.

[0048] As a lead plate 34, which connects to the bottom surface of theelectrode assembly 31, a configuration provided with a flexibledeforming piece 34A, as shown in FIG. 8, was used. A flexible deformingpiece 34A, which protruded outwards approximately 0.2 mm was used.

[0049] An electrode assembly rolled into a spiral shape with a separatorbetween electrodes and lead plates 33, 34 weld attached to both ends wasinserted in the external case 35 with the above configuration. Leadplates 33, 34 with a plurality of holes 39 and projections 310 providedat the periphery of the holes 39 were used. The electrode assembly wasinserted into the external case, a laser was applied to the indentationcorresponding to the projection 35 a provided in the bottom surface ofthe external case, and the lead plate 34 was weld attached to theexternal case 35. As a coating on the laser weld region at the outerbottom surface of the external case, Hitachi Manufacturing LTD. [JP-K28]was applied. After weld attaching the lead plate 33 connected to the topsurface of the electrode assembly to the sealing lid 37, electrolyte wasadded, and the opening in the external case was closed off with thesealing lid 37 to complete fabrication of a nickel cadmium battery.

Embodiment 2

[0050] Nickel cadmium batteries were fabricated by the same process asembodiment 1 except the lead plate connected to the bottom surface ofthe electrode assembly had no flexible deforming piece. The region ofthe lead plate for weld attachment to the external case was planar forthis battery.

Comparison Example

[0051] Nickel cadmium batteries were fabricated by the same process asembodiment 1 except the bottom surface of the external case had noprojection.

[0052] The following shows comparison of lead plate to external caseweld attach success ratios for batteries fabricated as described above.Batteries of Embodiment 1 100% Batteries of Embodiment 2  98% Batteriesof the Comparison Example  97%

[0053] From these test results, batteries of embodiment 1 and embodiment2 had lead plates and external cases reliably connected. In particular,there was no failure of lead plate to external case weld attach forbatteries of embodiment 1.

[0054] As this invention may be embodied in several forms withoutdeparting from the spirit of essential characteristics thereof, thepresent embodiment is therefore illustrative and not restrictive, sincethe scope of the invention is defined by the appended claims rather thanby the description preceding them, and all changes that fall within themeets and bounds of the claims or equivalence of such meets and boundsthereof are therefore intended to be embraced by the claims.

What is claimed is:
 1. A battery comprising: (1) a cylindrical shapedexternal case having a projection jutting from its inner surface; (2) anelectrode assembly inserted into the external case; and (3) a leadplate, which is connected to the electrode assembly, and which isconnected to the projection jutting from the inner surface of theexternal case by an energy beam applied to the external case fromoutside the external case.
 2. A battery as recited in claim 1 whereinthe external case is a circular cylindrical shape, and a projection isprovided at the center of the bottom plate of the external case.
 3. Abattery as recited in claim 2 wherein a spiral shaped electrode assemblyis inserted into the circular cylindrical shaped external case.
 4. Abattery as recited in claim 1 wherein a projection for connection to thelead plate is provided on a side-wall of the external case.
 5. A batteryas recited in claim 1 wherein the shape of the external case is arectangular cylinder, an elliptical cylinder, or a cylinder shapebetween rectangular and elliptical (super-elliptical).
 6. A battery asrecited in claim 5 wherein a spiral shaped electrode assembly is pressedfrom both sides to deform it into an ellipse and inserted into anelliptical external case.
 7. A battery as recited in claim 5 wherein anelectrode assembly, formed by cutting a plurality of positive electrodeplate and negative electrode plate sheets and stacking them withseparator in between, is inserted into a rectangular cylindricalexternal case.
 8. A battery as recited in claim 1 wherein the protrudingsurface of the projection provided on the external case is curved aroundthe central protrusion.
 9. A battery as recited in claim 1 wherein theprotruding surface of the projection provided on the external case jutsout in a conical shape.
 10. A battery as recited in claim I wherein aflexible deforming piece is formed on the lead plate as a result of aU-shaped cut-out around the flexible deforming piece, and the flexibledeforming piece is weld attached to the projection on the external case.11. A battery as recited in claim 10 wherein the flexible deformingpiece projects outward towards the projection on the external case. 12.A battery as recited in claim 10 wherein the external case is circularcylindrical shaped, the lead plate is cut from metal plate in a diskshape smaller than the inside of the external case, and the flexibledeforming piece is disposed at the approximate center of the lead plate.13. A battery as recited in claim 12 wherein the lead plate has holeswith projections around the peripheries of the holes, and theprojections are connected to the electrode assembly.
 14. A battery asrecited in claim 1 wherein anti-corrosive coating is applied to theregion of energy beam application outside the external case.
 15. Abattery as recited in claim 14 wherein the anticorrosive coating isconductive.